1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus.
2. Description of the Related Art
As a recording medium for storing a large amount of data, a magnetic disc such as a HDD using a magnetic method, an optical disc such as a CD or DVD using an optical method and a photomagnetic disc, etc. using a photomagnetic effect are used.
The optical disc using the optical method has to have a small bit (bit recording mark) size and a narrow track width in order to have a high-density recording capacity. However, because a spot size of light collected onto a disc so as to form a bit onto a recording layer thereon is restricted by diffraction limit, there is limit to improve a recording density.
Trends toward large storage in recording medium needs a new optical recording/reproducing method capable of overcoming the limit of the conventional optical recording/reproducing method. Recently, researches on near field recording/reproducing using a near field capable of improving a recording capacity epochally have increased.
Principals of the near field optical recording/reproducing will be described as follows. In light incident to a lens at an angle not less than a critical angle of the lens, when the light proceeds from an optically dense portion to an optically rare portion in a refractive index, the light is total-reflected. Herein, by the total reflection of the light, light having very low brightness exists on the surface of the lens, it is called an evanescent wave. By using the evanescent wave, it is possible to have high resolving power that could not have in the conventional far field due to absolute limit, namely, diffraction limit occurred by a light diffraction phenomenon.
A near field optical recording/reproducing instrument generates an evanescent wave on the surface of a lens by total-reflecting light in the lens, and accordingly data can be recorded and reproduced by coupling the evanescent wave to a disc.
As depicted in FIG. 1, the conventional near field optical recording/reproducing apparatus includes a swing arm 21 installed so as to perform a reciprocating rotation; an actuator 23 for rotationally driving the swing arm 21; and a head 30 installed at the end of the swing arm 21 in order to scan tracks of a disc 10 by being lifted above the disc 10 by air dynamic pressure.
As depicted in FIG. 2, the head 30 includes a lens unit having an objective lens 61 and a converging lens 62 separated from the objective lens 31 by a focus distance of the objective lens 31 and a slider 33 for installing the lens unit.
It is general to use a solid immersion lens (SIL) or a solid immersion mirror (SIM) as the converging lens 62.
In addition, in order to lift the slider 33 above the disc 10, an air bearing system (ABS) 36 for generating air pressure to the disc 10 and the slider 33 is installed at the bottom surface of the slider 33.
And, a radiating unit (not shown) for generating laser light in order to record/reproduce data onto the disc 10 as a recording medium, a light receiving unit (not shown) for sensing light reflected upon the disc 10 and an optical unit 40 for transmitting light to the head 30 are fixedly installed at the upper portion of the head 30.
A laser diode is used as the radiating unit, a photo diode is used as the light receiving unit, and the optical unit includes a beam splitter and a collimating lens, etc.
Herein, because light (L) to pass the objective lens 61 has to be vertically incident on the objective lens 61, a transmission path of the light (L) has to be bent, for that, a reflection mirror 41 or a prism, etc. is used.
In the conventional optical recording/reproducing apparatus, according to rotation of the swing arm 21 by operation of the actuator 23, the head 30 is moved above the disc 10.
Herein, the head 30 is in the flying state by the ABS 36 installed at the bottom surface of the slider 33, and data is recorded/reproduced onto/from the disc 10 according to the movement of the head 30.
The recording/reproducing process of the optical recording/reproducing apparatus will be described in more detail. In the process, the radiating unit generates laser light (L), the laser light (L) is transmitted to the reflection mirror 41 through the optical system, is incident on the objective lens 61 and is incident on the disc 10 through the converging lens 62.
According to the laser light incident on the disc 10, data is recorded on the surface of the disc 10. On the contrary, according to surface conditions of the disc 10, the laser light (L) is reflected, is transmitted to the light receiving unit through the converging lens 62, the objective lens 61, the reflection mirror 41 and the optical system, and accordingly data recorded onto the disc 10 is reproduced.
However, in the conventional optical recording/reproducing apparatus, when the optical unit 40 is installed at the actuator 23 and the head 30 includes only the reflection mirror 41, the objective lens 61 and the converging lens 62, because the laser light (L) generated in the radiating unit or light to be transmitted to the light receiving unit 40 has to pass above the swing arm (21), etc., optical errors may occur due to the long progress path, in addition, installation of the optical unit 40 is intricate.
In the meantime, in order to solve the above-mentioned problems, when the optical unit 40 is installed onto the slider 33, because a thickness and load of the slider 33 are increased, driving power of the swing arm 21 has to be increased, it is difficult to control accurately driving speed thereof due to that, and accordingly a performance of the optical recording/reproducing apparatus may be lowered.
In addition, because the slider 33 abutting above the disc 10 in moving may vibrate up and down according to the surrounding conditions, transmission error of laser light may occur due to the vibration.